Presensitized lithographic light-sensitive sheet construction



UnitedStates Patent" 3,136,637 PRESENSITIZED LITHOGRAPHIC LIGHT- SENSITIVE SHEET CONSTRUCTION Gerald W. Larson, St. Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Nov. 26, 1958, Ser. No. 776,597

9 Claims. (Cl. 96-75) use, the plate is first exposed to actinic light through a negative transparency or stencil to insolubilize the lightsensitive coating in the light-struck areas. Then the plate is washed with water and lightly rubbed to remove the remaining soluble portions of the coating. The plate :in this form is ready to be put on the press and is capable of printing satisfactorily. For long press runs, however, it is advantageous to render the imagemore durable through the addition of an abrasion-resistant cap or coating to the image areas. the application of a lacquer to these areas.

This has been accomplished by Thereby press life of the plate can be lengthened materially. The application of'such a strengthening material usually involves rubbing onto the plate surface a liquid containing a material which is strongly organophilic, tough and highly adherent to the exposed resin in the light-exposed areas. Said material thus becomes strongly adhered to the image areas. Such a material has sometimes been referred to as an image developer. 7

Since the advent of the metal-backed presensitized printing plates described in the aforesaid Iewett and Case patent, many have addressed themselves to the provision, 1

of materials which would satisfactorily serve as an image strengthener, i.e., the durable cap or coating in the image areas. Hall Patent No. 2,754,279 represents one successful and satisfactory solution.

However, the concept of reinforcing an image after exposure of the plate has inherent difliculties. The manner in which the image strengthener is applied to the plate surface can make a great deal of difference in the press life of the plate. Care is required. 'For example, when the image strengthener is applied properly, skillfully and uniformly, the plate may be used to reproduce many thousands of copies more than if it is applied poorly. Also, a poorly capped or coated image may not accept ink properly, and be worse than if no strengthener had been applied at all.

Oftentimes, however, the person shouldered with applying the image strengthener is the press operator himself,

or someone else other than a highly skilled platemaker. Such persons ordinarily are not adept at applying the image strengthener uniformly so as to obtain consistently f good results. Even skilled platemakers have difliculty in attaining consistency.

These problems often are further compounded by quality variations in the image strengtheners as supplied by manufacturers.

By and large, in attempting to minimize the dilficulties above mentioned, lithographers, manufacturers and suppliers of lithographic supplies, and others concerned have centered their efforts in the direction of attempting to obtain and provide superior image strengtheners which are more effective and easier to apply than those heretoresistant and wear-resistant. so that it will readily accept the oil-based inks used in 40' 3,136,637} Patented June 9, 1964;

fore known. Much time and money have been expended toward this end.

, Others, taking a somewhat different avenue of approach, have attempted to alter and' improve the strength and durability of light-sensitive resins, .e.g., by incorporating or reacting certain resinous materials therewith. Hodgens Patent No. 2,826,501, granted March 11, 1958, is an example. However, the selection of theresinous materials which can beso used is limited. Processing difficulties occur in manufacture of the resulting lightsensitive compositions, e.g., dilficulti'es arise in the selection and use of proper commercial solvents. Moreover,

invention has successfully provided a novel stable presensitized printing plate of markedly improved press life wherein there is no heed for the addition of any material to the image areas after exposure of the plate, or for any particular skill on the part of the person developing the plate in order to provide a printing plate of extreme long life. The provision of such a structure is a primary objective of the present invention. v

In attaining these and many other objects and advantages, many of which will be apparent from the following description, I provide a presensitized plate structure in which, as received from the manufacturer, the entire exterior surface is provided with the ultimate physical characteristics desired of the image areas in the exposed plate. That is, the exterior surface is hard, durable, abrasion- It is strongly organophilic lithography. When exposed to actinic light in the customary fashion, and then wiped or lightly rubbed with a processing composition involving common solvents, the exterior surface in the non-exposed areas, and the underlying unreacted sensitizer in said areas are quickly, easily and completely removed. An accurate sharpclear image thereby is defined, even in the case of fine half-tone images.

My invention has important utility beyond metalbacked presensitized printing plates, and beyond the printing field. Some of these will be brought out hereinafter in the specific examples which follow.

Generally,-the novel plate or sheet structures hereof comprise a base sheet having coated thereover a stable light-sensitive resin layer, e.g., a light-sensitive diazo resin, which upon exposure becomes insolubilized from its initial state. The surface of the base sheet underlying the lightsensitive material is receptive to the formation of a firm bond with the in situ insolubilized light-sensitive material.

7 Coated over and in contact with the light-sensitive material is an actinic light-transmittable film or layer of a hydrophobic water-insoluble solvent-softenable resin. The manner in which the present invention is practiced in overcoming thelong-known deficiencies in the prior art, as well light-sensitive sensitizer layer 12. Where necessary, surface 11 may involve a treatment which protects the sensitizer layer 12 from beingdegraded by any degradative V i W 7 V V characteristics in the base sheet 10. Overlying said lightsensitive layer 12 is an overcoating or layer of an organophilic hydrophobic water-insoluble substantially contin uous, solvent-softenable organic resin film .or coating 13.

FIGURE 2 shows the sheet construction of FIGURE 1 afterit has been. exposed to actinic light through a transparency or stencil. During exposure the actinic light passing through the transparency also passes'through resin coating 13 and strikes. the light-sensitive layer in the image areas 12a. I In the latter areas the sensitizer reacts to become insolubilized-and firmly adhered'to the underlying surface 11 of the base sheet 10.. Also in said exposed areas lthe-light-reacted resin firmly bonds .the overlying resin layer 13. In the non-exposed areas 12b the sensitizer remains unreacted and soluble.

Finally, FIGURE 3 shows the sheet construction of FIGURE 2, after it has been wiped or lightly scrubbed with processing solvent selected with respect to the par- ,ticular material of which layer 13 is composed, and which contains a solvent for the unexposed light-sensitive material. When the plate surfaceis so treated and lightly scrubbed, the resin layer 13 is softened and breaks away cleanly along'the lines of demarcation between the exposed and unexposed areas to leave resin areas 13:: coinciding withareas 12a-of exposed reacted sensitizer. The .unexposed light-sensitive material in the non-light struck areas is also washed'away from the plate baring the underlying surface 11, which, in the case of a printing plate, 1 preferably is-hydrophilic in character.

The plate, then, and without necessity of further proc- .essing is ready for mounting on the printing press. 7 The .lmage areas are strongly organophilic, firm and Wear-resistant.

-- It is to be noted that the purpose of the drawing is for illustrative purposes only, and it is not intended that the various layers and components of my plate constructions In the examples the concentrations of all coating solutions or compositions are based on weight of material in grams dissolved or dispersed per 100 milliliters of total volume of solution and/or dispersion.

. Example I A solution is first prepared by dissolving polyvinylformal resin in ethylene chloride solvent to yield approximately an 8 percent solution. A suitable polyvinylformal resin has a polyvinyl alcohol content of from about 7-9 .percent and a polyvinyl acetate content of from about 95-13 percent, and a percent ethylene chloride solution thereof has a viscosity of about 40-60 cps. at C.

A phthalocyanine pigment, e.g., Monastral Fast Blue BC available commercially from the Du Pont Company,

- is then coated under subdued light, e.g., yellow light, with the coating composition previously prepared. The presensitized plate construction is manufactured continuously in accordance with the specific example of Jewett and Case Patent No. 2,744,066. Briefly, such lithographic plate structure is prepared by cleaning a smooth-surfaced aluminum sheet, for example with trisodium phosphate followed by treatment with nitric acid solution and rinsing in water. The; sheet is then treated with an aqueous silicatesolution and washed clean of any remaining watersoluble materials. An initially water-soluble light-sensitive diazo resin, e.g., a p-diazodiphenylamine-formaldehyde resin, is then coated over the silicate treated surface.

insoluble character.

are forwarded to customers. ducted under subdued light.

the surface of the yet sensitized plate.

tional solvent mixture.

The continuous web of presensitized plate is then flow coated 'by passing it (sensitized surface outward) around a roller partially immersed in the coating solution at a web speed of about 1.5 feet per minute. The temperature of. the coating solution in the tank is maintained at room temperature. A dry coating-weight of about 50 mg/ft is applied, the exact coating weight applied being determined by the speed of the web, the temperature of the room and viscosity of the coating solution.

The thus coated web, coated side uppermost, is thenair dried, theweb being passed alongside a vented hood. At normal room temperature the overcoating dries within a veryfew minutes to its permanently organophilic water- The web so prepared is then die-cut to standard plate sizes and packaged in light-proof containers in which they The entire operation is con- The customer in using the plate removes the same from its package, under subdued light, and then exposes the plate to actinic light through a photographic negative or a stencil. v No particular care need be exercised in handling the plate. It matters not, for example if finger prints and/onmoisture droplets inadvertently occur on If such do occur,.the plate simply is wiped clean and processing resumed.

The plate maybe exposed in the manner described in the aforesaid Jewett and Case Patent No. 2,714,066. For example, exposure of the plate to a 35 ampere carbon arc at a distance of about 24 inches for a time of from 1 to Z minutes provides suitable exposure for the light-sensitive diaizo resin in the light-struck areas. By the exposure, the sensitizer in the exposed areas is converted to a water-insoluble character. The physical properties of the resin overlayer in said exposed areas do not seem to change.

Following exposure, and still under subdued light, a Solvent mixture of 2 parts isopropanol and 1 part water by volume is poured liberally onto the plate'surface and spread'uniformly thereover by wiping gently with a soft sponge or cloth mounted on a firm backing such as'a wood block. After a few seconds a gentle rubbing action removes the polyvinyl-formal resin coating from the unexposed areas while virtually none is removed in the exposed .areas. The area being worked should be wet at'all times and it may be necessary to add addi- After the resin coating has been removed, which takes only a few seconds, the entire surface of the plate is-then, treated by wiping it thoroughly with an aqueous desensitizing and gumming solu- ..tion, for example,. a slightly acidified water solution of gum arabic. Thereby any diazo resin remaining in the non-image areas is removed and the underlying silicate treated aluminum .surface in these areas is bared.

The image will be clearly visible on the plate, by virtue of the blue color imparted by the pigment, and clearlywill contrast with the treated aluminum surface in the non-image areas. It is thus extremely easy to determine when the image is clearly and accurately brought out.

Without further treatment the plate is then mounted on a conventional. offset lithographic press for printing.

When optimum adjustments have been made on the press so that the press is adjusted to the least pressure consistent with quality printing, over 200,000 line copies consistently have been produced with a single lithographic plate prepared as' described in the present example. So little change and diminution of the image occurs'that evena' skilled printer can hardly tell the difference between the first few reproductions and the i two hundred thousandth copy. Over 50,000 accurate reproductions of fine half-tone originals have been produced from a single plate,

.Although the initial abrasion-resistant organophilic nature of the resin overlayer does not seem to change upon i sensitive resin materials. ment employed with the resin is maintained at a level resin image is unreinforced.

exposure ofthe plate, the resin overcoating nevertheless is bonded extremely well to the underlying in situ insolubilized sensitizer. This is further evidenced by the "fact that when the image is being processed with a solvent solution for the resin layer, the resin layer breaks away cleanly and sharply at the line of demarcation between the image and non-image areas and is readily -removed from the latter. Although I do not know with exactness just why this occurs, and without intending to be limited by any theories, 1 hypothesize that there is some physical and/ or chemical interaction at the interface of the light-sensitive material and the resin overlayer which occurs when the light-sensitive material is exposed. Then when the solvent, which softens the overlayer, is applied it permeates the thin overlayer film 'and effectively undermines the overlayer in the nonimage areas by the action of the solvent on the unex- Thereby the image is rendered visible processing. Further, I have found that the presence of a pigment s eemsto facilitate a clean sharp break at the line.of demarcation between the image and non-image areas: Of course, the pigment employed must be such as 'totransmit the actinic light which must pass through the resin overlayer in order to strike the underlying light- Ordinarily the amount of pigsufficient to provide a clear contrast between image and background when the sheet is processed. This amount is usually something less than about 50 percent by weight act the resin, 25 percent being preferred in the printing plates hereof.

In the. preceding example, the. coating weight of the pigmented polyvinylformal resin overlayer was about 50 mgl/ft Although I prefer to maintain a coating weight of from about 50-70 mg./ft. when employing this overlayer composition, satisfactory plate structures a very heavy film may not fracture sharply and clearly at the line of demarcation between the image and nonimage areas yielding a distorted printing image. In

desired, it may be desirable to employ somewhat heavier coatings inprinting operations involving the former than 'can be satisfactorily used in half-tone work. On the other hand, I have made successful plates in accordance with the present example where the coating weight of' the polyvinylformal resin was as lowas about 3.6 mg./ft'. while yet providing significant improvement in presslife over a corresponding plate wherein the diazo Significantly, the thickness of a polyvinylformal resin coating having a weight of about 3-4 mg./ft. is in-the order of only about one millionth of an inch, i.e., 0.001

, mil. A rather heavy coating weight of 120 mg./ft. has a thickness in the order of about four one-hundred-thousandths of an inch, or 0.04 mil. Thus, in any event the resin overcoatings in the structures hereof are quite thin.

While the present example has illustrated the use of i polyvinylformal as vtheresin overlayer, many other organophilic hydrophobic water-insoluble solvent-softenable organic resin compositions are also suitable. These include various vinyl polymers, such as polyvinylbutyral,

fied by alkyd re sins,-polyamide resins, phenolaldehyde resins, urea-aldehyde resins; other polymers such as cel- 'lulo se acetate butyfate, polyalkylene-polysulfide resins,

various organic silicon containing resins, etc. Various rubbery compounds such as Buna-N, Buna-S, neoprene and natural crepe are suitable. Natural occurring resinous materials such as shellac can also be used. Various compatible mixtures of the above mentioned and other similar and equivalent resin materials can be used.

The processing solutions to be used in processingthe various sheet constructions hereof, after they have been exposed, should have certain'characteristics. Preferably the processing solution exerts a slight but not vigorous solvent or swelling action on the overlayer composition,

is an active solvent for the unreacted sensitizer, but has little or no effect on the light-reacted sensitizer. Ordina'rily a mixture of two or more (preferably miscible) liquids is necessary to provide a processing solution having these desired characteristics. However, an operable processingsolution can be found for any combination of sensitizer and resin overlayer employed, although some amount of rudimentary experimentation may be necessary. As ageneral rule, a suitable processing solution can'be obtained by combining a first component which .exerts at least a partial solvent or swelling action on the i just indicated, other processing solutions, which can he arrived at by judicious selection, may also be suitable.

'The isopropanol-water processing solution' of; Example I is such an instance, neither the water nor isopropanol by itself exerting any substantial solvent action on the polyvinylformal resin.

The following table will further illustrate the solvent from which various resin overcoating compositions are applied, and an appropriate processing solution therefor in a plate construction hereofcontaining the diazo resin of Example I. Where indicated in processing solutions, ratios are by volume; I

I overcoating resin composition Application Processing solution solvent Polyvinylchloride, Buna-N Methyl Water saturated with mixture (55:45) (Geon ethyl methyl ethyl Polyblend 503, B. F. ketone ketone. Goodrich).

Polyvinylchloride-polyvinyl do Acetonitrile-water,

acetate copolyrner (91% 2:1 ratio. polyvinyl chloride) (VAGH, Bakelite Corporation). Pplyamide resin (nylon) Methanol. Isopropanol-water, (Zytel 69, E; I. du Pont 1:10 ratio.

, de Nemours & 00.). i Cellulose acetate butyrate Methyl Ethanol-water, 1:2 (48% butyryl) (EAB-500- ethyl ratio;

5, Tennessee Eastman ketone. Corp). Y

Polytrifiuorochloroethylenedo Acetone-water, 3:1 vinylidinefiuoride copol w I 1 ratio. mer (Kel-F 800, Minnesota Mining & Mfg. 00).; 1 .Bolychloropene (Neoprene Ethylene Water alone.

CG, E. Ltdu Pont de chloride. 7 1 7 Nemours & 00.). y 1

Bolyvinylacetate (AYAT/i Methyl Isopropanol-water,

Bakelite Corporation). ethyl 1:2 ratio.

Buna-N rubber (Hycar OR- do Isopropanol-water,

15, B. F. Goodrich &'Co.). 2:1 ratio.

Polyvinylbutyral (B72A', Methanol Do.

Shawinigan Resins. Corporation) Methyl, phenyl polysiloxane Toluene -Is0propanol-water,

silicone resin (Dow-Corn- 1:1 ratio. ing Corporation DC-840).

Epoxy resin reaction product Methyl Acetone-water,

of bis-phenol A and epiethyl 1:1 ratio.

, chlorohydrin (EKRD ketone.

2003, Bakelite Corporation).

While Example ,I is directed to a presensitized metalbacked printing plate, printing plates having backings other than metal can also be prepared in accordance with the present invention. The following example illustrates .a paper-backed plate.

.. Example 11 a ,A light-sensitive resin, which is initially soluble in an 'organic solvent, is first prepared. An aqueous solution of the p-diazodiphenylamine-formaldehyde resin utilized in the, plate structure of Example I, and described with specificity in Jewett and Case Patent No. 2,714,066 is 'addedto a chemical equivalent, based on the resin content of the solution, of p-toluenesulfonic acid. By a reaction between the resin and the acid the p-toluenesulfonate salt of the resin is formed and oils out of the aqueous medium as a viscous tar-like resinous material. The reaction product is separated by decanting and washed with water.

On standing, it dries to a glassy solid amber-colored state.

It readily dissolves in methanol, but is only very slightly soluble in most other common organic solvents and in Water: Upon exposure en masse to actinic light it becomes insoluble to methanol and turns slightly blue-green from its initial amber color. When exposed in thin films,

the characteristic blue-green color is barely visible or in very thin films'is not visible at all.

A 2 percent methanol solution of the light-sensitive "resinous product just described is prepared. A sample of 45 lb. vegetable parchment, available ,from the West Carrollton Parchment Company, of West Carrollton, Ohio, is sensitized with the previously formed light-sensitive resin solution by wiping the surface of the parchment with acot ton cloth saturated with the resin solution, The treated surface is then allowed to air-dry.

' The thus sensitized surface of the parchment is then "overcoated by coating the surface with the pigmented polyvinylformal-ethylene chloride solution described in Example I, at a dry coating weight of about 30 mg./ft.

the thickness of the overcoating being about 0.01 mil.

The overcoating is then air dried. Upon exposure of the plate through a transparency as outlined in Example I,

followed by processing with the isopropanol-water soluit is found to print clean clear copies.

It will be seen that the light-sensitive material employed in Example II is of different character than the water-soluble light-sensitive resin employed in. Example I. A particular advantage in the present invention resides in that virtually any initially soluble light-sensitive material, which insolubilizes upon exposure, can be employed in conjunction with the resin overcoatings hereof so long as the latter are capable of being coated on, i.e., not repelled by, the light-sensitive material. The in situ created adhesion between the light-sensitive layer and the resin overlayer, when the former is exposed and insolubilized, appears to occur largely irrespective of the particular type of light-sensitive material employed. Since the resin overlayer provides the printing surface, lightsensitivematerials may now be employed in lithographic plates, even though in and of themselves, they inadequately provide a printing image. Stability of the sensitizer can be high sothat the base sheet coated therewith is presensitized, i.e., the sensitized sheet can be stored for substantial periods of time with the sensitizer remain-" ing stably soluble and light-sensitive. The light-sensitive diazo resins described in the preceding examples are highly stable and serve as preferred sensitizers in the sheet constructions hereof.

Although the previous'examples have dealt with the lithographic printing art, the present invention has marked utility in fields diverse from the printing field. In many fields of endeavor it is desiredto have some pictorial representation or message adhered on a backing sheet or plate. For example, in the preparation of labels,

particularly metal labels, templates, registration tags,

for use iii-letterpress printing, an image of an acidresistant material must be adhered to the surface of the plate.

It has long been desired to utilize photographic techniquesto bring out a message or pictorial representation on backing structures in the above-mentioned and other fields. However, this has been largely impractical heretofore because the light-sensitive materials which form the image or pictorial representation (the background for such image or representation wherethe resulting image is negative) have not had suitable physical characteristics for the conditions under which they would be.used. By the present invention I am able to provide photographically an image area with any of widely diverse physical qualities appropriately selected with the particular end use in mind. The following examples illustrate a few of these, the next example illustrating the use of my invention in providing a novel printed circuit board.

Example III The copper surface of a construction, consisting of a one mil layer of copper adhered to a non-conducting phenolic resin sheet, was cleaned with scouring powder.

' Said surface was then coated, by dip-coating techniques, with a diazo-p-toluenesulfonate sensitizer resin described in Example 11. Upon air drying, a comparatively heavy diazo resin coating resulted which was clearly visible by its slight yellow tinge. Through dip coating, the light sensitized base was then overcoated at a dry weight of -'tizer were removed from the non-image areas, the resin overlayer breaking away cleanly at the lines of demarcation between image and non-image areas.

When the resulting sheet was placed in a solution of 40% ferric chloride at 80 C., the copper etchedaway in the non-image areas from which the polystyrene coating had been removed. However, no undesirable etch of the copper in the image areas, protected by the polystyrene overcoating, occurred. The remaining copper was found to be patterned in the correct 1 form of the original to serve as a printed circuit. On the other hand, when the polystyrene layer is omitted the diazo resin itself does not effectively resist etching in the image areas.

Polystyrene was chosen in the above example because of its insensitivity to water and acid. Similarly, a nonoxygenated resin suchas polyvinylchloride or a rubber composition such as Buna-N or neoprene can be used. In

other etch resist applications it might be desirable to use a fusible heat curing resin, such as an epoxy resin,'which is cured before etching the plate. In employing a curable 'It is noted that the various processing solutions noted for the various resin overlayer compositions in the preceding table can also be employed for those respective compositions in plate structures containing the sensitizer of the present example.

V A coating compositionwas first preparedby dissolving resin system care should be taken to select a system which will not undesirably'degradate the light-sensitizer.

' The next example illustrates the preparation of a metalbacked label in accordance with myinvention.

7 Example IV parts of methyl ethyl ketone following which 1.5 parts of a green phthalocyanine pigment (Du Pont Monastral Fast Green G Powder) was milled into the solution. The composition was then coated over the diazo resin surface of a presensitized lithographic plate like that employed in Example I, prepared in accordance withJewett and Case Patent No. 2,714,066. A dry coating weight of 135 mg./ft. provided good color depth. After the resin overlayer had been air dried the sheet was exposed to actinic light through a transparency of the desired message. The image was then processed with a solution of isopropanol-water (2:1 by volume) to yield a reverse.

green colored image having pleasant contrast with the aluminum. The image showed excellent durability to weathering.

Thus sheet constructions containing images of a wide variety of colors can be made, in accordance with the procedures hereof, by incorporation of suitably colored actinic-light transmittable pigments into the resin overlayer. Combinations of such pigments can be used, e.g.,

, where a resulting black color is desired. It is to be noted that the exposure time may vary with the color and type of pigment selected. For example, somewhat longer exposure times may be required in the case of yellow and red than with other pigments.

My invention is also valuable in proofing color separation negatives preparatory to color lithography. In color 3 printing, color separation negatives are prepared photographically in three or more colors. Each color separation negative is used to prepare a printing plate from which reproductions are printed in sequence using appropriately colored inks. In proofing the color separa 1 tion negatives by conventional methods, it is necessary to prepare all of the printing plates, to set up the printing press for operation, and then'actually to print all of the colors in the proper sequence and registration. All

this is necessary to determine whether the original color separation negatives were true and accurate. Such conventional proofing procedures are extremely costly and timeconsuming. With each correction, one or more new plates has to be prepared and the entire operation repeated until the desired result is achieved.

In accordance with my invention, it is possible to complete the color proofing to a degree at least equal to that by which the color in the non-image areas is removed.

10 area is adjusted to provide the same color-density to be printed from the respective inks. Thus very accurate color proofs result. The following example illustrates the preparation of a color separation proof hereof.

Example V In accordance with Palmquist Patent No. 2,786,778, a

i one mil thick film of biaxially-oriented polyethylene .ter-

ephthalate (Mylar) is vapor coated to provide thereon a thin, invisible hydrophilic treatment or layer of silicon monoxide. The silicon monoxide surface is then coated with the diazo resin solution described in.Example H. The coating weight is quite light so that, .upon exposure, no visible blue color will be imparted by the diazo so as to disturb the delicate color balance required in color proofing. Preferably, the amount. of diazo applied is just under that which would impart a visible color efiect upon exposure. I

The diazo surface is then overcoated with a polyvinylformal containing a suitable transparentpigment, in a manner similar to that described in Example 'I. Since color is of primary importance the pigment loading will be most useful in the rangeof 30 to percent of total solids in the overlayer. The coating weight required will be dependent upon the color density desired. For use in duplication of 3-color process printing reproductions, reflective optical densities measured through complementary color filters will be in the range of 1.0 to 1.5, and the respective coating weights will be adjusted to attain that range. Acoating weight of 6O to 120 mg./ft. ordinarily is an optimum weight depending upon the specific desired color levels. Suitable pigments for use in each of the three-color constructions are: cyan, e.g., Monastral Fast Blue BC, available from the Du Pont Company; magenta, e.g., Alkali Resistant Red RT539-D,. .available from the Du Pont Company; and yellow, e.g., fBenzidine Yellow Dye D-2840, available from the Sherwin- Williams Company. I v

.Since a transparent backing is employed on the lightsensitive sheet hereof a black backing is required behind the light-sensitive sheet during exposure in order to reduce halation in the exposed image.

In use, each of'the three color sheets is exposed through its corresponding color separation negative. The sheet is then processed, as previously described, with a solution of isopropanol-water in a 2:1 ratio to remove the pigmented overlayer from the non-image areas to leave the-latter clear and colorless. Thereby an image is de- Respedtively colored sheets result, each of which is fined which corresponds to the single color proof made by mountingthe proper plate on a press and printing. When the three proofs aresuperposed in registry on a white background an accurate proof is obtained of the 3 -color print which would result from forming printing plates of the negatives and printing from those plates.

overlayers which are ,opaque, i.e., wherein the'pigment in the overlayer is opaque, can also be used in structures hereof employing transparent backings. In such construction the sheet is exposed from the reverse side (through the transparent backing sheet). Such a concurate color proof of the original negatives results The I entire proofing procedure can be accomplished in a mat- In preparing light-sensitive sheet constructions for use;

in color-proofing, I employ a colorless "transparent backing sheet for the light-sensitive layer and resin overcoating, which preferably is dimensionally stable. The overcoating in-each sheet contains the same respective pigment, or equivalent thereof, as that containedin the 1 printing ink. The amount of pigment contained per unit struction is desirable, for example, in providing the black print for proofing 4-color process printing. Carbon black is a suitableopaque pigment in this construction.

A construction of. the present example coating, opaque black pigment: is also useful in preparing a positive transparency from a negative transparency or-vice versa without necessity of employing the usual photographic film.

Although in the previous examples various specific organic hydrophobic organophilic water-insoluble solvent-softenable resin overlayers have been disclosed, it is to be understood that many of the compositions disclosed in the respective examples can be used in the constructions described in other examples. Theselection of the appropriate overlayerfcomposition will be governed primarily by the final properties desired of the with the aid of variousillustrative examples.

image-areas, as respects the end use to which the exposed and processed'sheet structure hereof will be put. Herein, I have provided novel means for providing an accurate pictorial representation or messageon a backing sheet,' wherein the character of the pictorialrepresentation or message, or the background thereof, can be widely varied to suit the particular enduse desired of the overlying at leastone surface of said sheet in contact therewith, and over and in direct contact with said sensitizer layer a thincontinuous hard durable abrasionresistant and wear-resistant coating composed predominantly of an organophilic hydrophobic water-insoluble solvent-softenable resinous polymer, said coating having a thickness of at least about 0.001 mil and containing tact with saiddiazoresin coating .athincontinuous pigmer ted coating of water-insoluble polyvinylformal resin in an amount of from about 50-70 mg./ ft. the amount of pigment in said coating not exceeding about percent .by weight thereof; said diazo resin being characterized that, upon exposure of theiplate to ultra-violet light through a transparency, it will react in the exposed portions to form an image ofWater-insoluble, hydrophobic and organophilic material which is tightly bonded to said permanently hydrophilic, 7 surface; said polyvinylformal resin coating being transparent to actinic light, being isolated from bonding contact with said aluminum sheet j and being intimately associated with said diazo resin and adherently bonded thereto, and further remaining waterinsoluble and organophilic upon subjection thereof to the products evolved -by said diazo resin upon exposure of said plate to actinic light.

I 6. A presensitized lithographic plate comprising a metal base sheet, a soluble light-sensitive diazo resin sensitizer layer overlying at least one surface of said sheet in contact therewith, and over and in direct contact with said sensitizer layer a thin continuous hard durable abrasion-resistant and wear-resistant coating composed predominantly of an organophilic hydrophobic waternot more than about 50 percent by weight of pigment;

said sensitizer layer upon exposure of the sheet to actinic light through a transparency reacting in the exposed areas and becoming insolubilized and firmly bonded to said surface of said base sheet; said abrasion-resistant and wear-resistant coating being isolated from bonding con-- tact with said base sheet and being intimately associated with andadherently bonded to said sensitizer layer, and further remaining abrasion-resistant and water-insoluble upon subjection thereof to the products evolved by said sensitizer upon exposure of said sheet to actinic light, 7 and being firmly bonded in said exposedrareas, while being readily removable with unexposed sensitizer in areas not light-exposed.

2. The pre-sensitized sheet of claim 1 wherein said abrasion-resistant and wear-resistant coating is composed entirely of said resinous polymer. g

3. A presensitized light-sensitive sheet construction comprising an aluminum sheet having a well-bonded treatment on one surface thereof, a soluble light-sensitive diazo resin material over and in contact with said surface treatment, and a thin continuous abrasion-resistant coating composed predominantly of water-insoluble polyvinylformal resin overlying and in contact with said diazo resin layer; said coating of polyvinylformal resin having a thickness of at least about 0.001 mil, being transparent to actinic'light, containing not more than about 50 percent by weight of pigment, and being isolated from bonding contact with said aluminum sheet and being intimately associated with and adherently bonded to said diazo resin layer; said coating further remaining abrasion-resistant and water-insoluble upon subjection thereof to the products evolved by said diazo resin upon exposure of said sheet construction'to actinic light, said treatment being characterized in that it causes an in situ light-reacted diazo resin firmly to bond to said aluminum sheet.

4. The construction of claim 3 wherein said coating of polyvinylfo rmal resin contains a colored pigment and related uses comprising an aluminum sheet having on at least one surface thereof an extremely thin layer of the reaction product of said aluminum sheet and an aqueous solution of an alkali metal silicate, providing a permanently hydrophilic surface, a thin coating of a water-soluble light-sensitive diazo resin over and in con tact with said hydrophilic surface, and over and in coninsoluble solvent-softenable resinous polymer, said coating having a thickness of at-least about 0.001 mil, being transparent to actinic light and containing not more than about .50 percent by weight of pigment; said sensitizer layer upon'exposure of the sheet to actinic-light through a transparency reacting in the exposed areas and becoming insolubilized and firmly bonded to said surface of said base sheet; said abrasion-resistant and wear-resistant coating being isolated from bonding contact with said base sheet and being intimately associated with and adherently bonded to said sensitizer layer, and further remaining abrasion-resistant and water-insoluble upon subjection thereof to the products evolved by said sensitizer upon exposure of said plate to actinic light, and being firmly bonded in said exposed areas, while being readily removable with unexposed sensitizer in areas not light exposed. a

7. A presensitized' metal lithographic plate comprising an aluminum sheet having on at least onesurface thereof an extremely thin layer of the reaction product of said aluminum sheet and an aqueous solution of an alkali metal silicate, providing a permanently hydrophilic surface, a thin coating of a water-soluble lightsensitive diazo resin over and in direct contact with said hydrophilic surface, and over and in contact with said diazo resin a thin continuous hard durable abrasionresistant and wear-resistant coating of an organophilic hydrophobic water-insoluble solvent-softenable resinous polymer, said coating having a thickness of at least about 0.001 mil, being transparent to actinic light and contain- 55 ing not more than about 50 percent by weight of pigment; said 'diazo resin being characterizedin that, upon exposure of the plate to ultraviolet light through a transparency, it will react in the exposed portions to form an image of water-insoluble material which is tightly bonded to said permanently hydrophilic surface; said abrasion-resistant and wear-resistant coating being transparent to actinic light, being isolated from bonding contact with said aluminum sheet and being intimately associated with said diazo resin and adherently bonded thereto, and further remaining abrasion-resistant water-insoluble and organophilic upon subjection thereof to the products evolved by said diazo resin upon exposure of said plate to actinic light, and being firmly bonded in said exposed areas, while being readily removable with unexposed sensitizer in areas not light-exposed.

8. A presensit'ized light-sensitive sheet construction comprising a base sheet, a light-sensitive diazo resin sensitizer layer overlying at least one surface of .said sheet continuous abrasion-resistant coating composed predominantly of water-insoluble polyvinylformal resin, said coating having a thickness of at least about 0.001 mil, containing not more than about 50 percent by weight of pigment, and being isolated from bonding contact with said base sheet by said coating of diazo resin, said coating further remaining water-insoluble and organophilic upon subjection thereof to the products evolved by said sensitizer upon exposure of said sheet construction to actinic light; said diazo resin layer, upon exposure of the sheet to actinic light through a transparency, reacting in the exposed areas and becoming insolubilized and firmly bonding said resin coating to said base sheet, the portions of said resin coating in the areas not exposed to light being readily separable from the portions thereof in exposed areas and being removable with the remaining unexposed sensitizer upon mild rubbing with an aqueous solvent solution.

9. A presensitized light-sensitive sheet construction comprising a dimensionally-stable transparent and colorless base sheet, a stable soluble light-sensitive diazo resin sensitizer layer overlaying at least one surface of said sheet in contact therewith, said sensitizer layer, upon exposure of the sheet to actinic light through a transparency, reacting in the exposed areas and becoming insolubilized and permanently bonded to said surface of said base sheet and being transparent and essentially colorless in said areas, and said sensitizer having thereover and in contact therewith a thin continuous abrasion-resistant coating of pigmented Water-insoluble polyvinylforrnal resin, the amount of pigment in said coating not exceeding about 25 percent by weight thereof, said coating having a thickness of at least about 0.001 mil, and further remaining water-insoluble and organophilic upon subjection thereof to the products evolved by said diazo resin upon exposure of said sheet construction to actinic light.

References Cited in the file of this patent UNITED STATES PATENTS 1,342,590 Lovejoy June 8, 1920 1,992,965 Rowell Mar. 5, 1935 2,173,480 Jung Sept. 18, 1939 2,311,888 Toland et a1. Feb. 23, 1943 2,714,066 Jewett et a1 July 26, 1955 2,732,304 Vanselow et a1. Jan. 24, 1956 2,754,279- Hall July 10, 1956 2,760,893 Plambeck Aug. 28, 1956 2,791,504 Plambeck May 7, 1957 2,804,388 Marron et a1. Aug. 27, 1957 FOREIGN PATENTS 371,153 Great Britain Apr. 21, 1932 740,165 Great Britain Nov. 9, 1955 761,493 Great Britain Nov. 14, 1956 1,090,398 France Oct. 20, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent Non 3 136 637 June 9 1964 Gerald W" Larson It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as aorrected below.

Column 12 line I, after "continuous" insert abrasion-resistant Signed and sealed this 4th day of May 1965 .SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A PRESENSITIZED LITHOGRAPHIC SHEET COMPRISING A BASE SHEET, A SOLUBLE LIGHT-SENSITIVE DIAZO RESIN SENSITIZER LAYER OVERLYING AT LEAST ONE SURFACE OF SAID SHEET IN CONTACT THEREWITH, AND OVER AND IN DIRECT CONTACT WITH SAID SENSITIZER LAYER A THIN CONTIOUS HARD DURABLE ABRASIONRESISTANT AND WEAR-RESISTANT COATING COMPOSED PREDOMINANTLY OF AN ORGANOPHILIC HYDROPHOBIC WATER-INSOLUBLE SOLVENT-SOFTENABLE RESINOUS POLYMER, SAID COATING HAVING A THICKNESS OF AT LEAST ABOUT 0.001 MIL AND CONTAINING NOT MORE THAN ABOUT 50 PERCENT BY WEIGH T OF PIGMENT; SAID SENSITIZER LAYER UPON EXPOSURE OF THE SHEET TO ACTINIC LIGHT THROUGH A TRANSPARENCY REACTING IN THE EXPOSED AREAS AND BECOMING INSOLUBILIZED AND FIRMLY BONDED TO SAID SURFACE OF SAID BASE SHEET; SAID ABRASION-RESISTANT AND WEAR-RESISTANT COATING BEING ISOLATED FROM BONDING CONTACT WITH SAID BASE SHEET AND BEING INTIMATELY ASSOCIATED WITH AND ADHERENTLY BONDED TO SAID SENSITIZER LAYER, AND FURTHER REMAINING ABRASION-RESISTANT AND WATER-INSOLUBLE UPON SUBJECTION THEREOF TO THE PRODUCTS EVOLVED BY SAID SENSITIZER UPON EXPOSURE OF SAID SHEET TO ACTINIC LIGHT, AND BEING FIRMLY BONDED IN SAID EXPOSED AREAS, WHILE BEING READILY REMOVABLE WITH UNEXPOSED SENSITIZER IN AREAS NOT LIGHT-EXPOSED. 